FIGS. 1 and 2 illustrate a known pre-assembled fuel pump module 10 for an automotive vehicle being inserted into a liquid fuel tank 12 through an access hole 14 defined by a peripheral edge 16 of a tank wall 18 that defines an interior or fuel chamber 20. The pump module 10 has an elongated electric fuel pump 22 disposed typically in the fuel chamber 20 when assembled and a substantially cylindrical flange 24 attached to the fuel pump 22 via a pair of parallel posts of a bracket 26. When fully assembled to the tank 12, the flange 24 engages salably to the peripheral edge 16 of the fuel tank wall 18, and the pump 22 is suspended within the fuel chamber 20 from the flange 24, and bracket 26.
The known fuel pump module 10 has an elongated fuel level measurement device 28 that sends a fuel level signal, via a pair of electric wires 30, to a fuel level indicator or meter typically mounted to an instrument panel of the vehicle (not shown). The wires 30 are connected to a variable resistor 32 on a card 34 snap fitted or seated within a plastic base 36 pivotally connected to the bracket 26. The pair of wires 30 extend through the flange 24 projecting outward from the tank 12.
An elongated wiper-type arm 38 has a base end 40 bent at an approximate right angle and carried pivotally by the plastic base 36 to pivot about an arm axis. An opposite distal end 42 of the wiper arm 38, also bent at an approximate right angle, pivotally carries a buoyant or hollow plastic float 44 that pivots about a float axis that is substantially parallel to the arm axis.
The buoyant float 44 is generally planar or low-lying and rectangular or cylindrical in shape and floats on the surface of fuel contained within the tank 12. As the fuel level changes, the float 44 rises or lowers with the fuel surface causing the wiper arm 38 to pivot at the base end 40, thus wiping or sweeping electrically conductive contacts 46 across contacts 48 of the variable resistor 32 producing a fuel level signal carried by the wires 30 to the fuel level indicator (not shown). The length of the wiper arm 38 is dictated by the shape or depth of the tank 12. That is, the wiper arm 38 must be long enough to allow the float to float upon the surface of fuel between a minimum and maximum elevation (i.e. Empty to full fuel tank conditions).
The variable resistor 32 has a series of contacts 48 imprinted upon the circuit board or card 34 and generally arranged side-by-side forming a semi-circular or arcuate orientation to preferably coincide with the pivoting axis of the wiper arm 38. Preferably the card 34 has a ceramic substance. The resistor 32 is connected electrically to one of the two wires 30. The second wire is electrically connected to a semi-circular or arcuate contact 50 also imprinted upon the card 34 and preferably coinciding with the pivot axis. The contact 50 is spaced radially from the resistor 32 and the series of contacts 48 and extends circumferentially with the series of contacts 48 so that the electrical contacts 46 mounted on the bottom side of a non-conductive or plastic saddle 52, attached to the base end 40 of the wiper arm 38, engage and electrically bridge or connect the neutral contact 50 with a predetermined one, or a few, of the series of contacts 48 as the wiper arm 38 is swept across the card 34 by the remote buoyant float 44 responding to the varying fuel level.
The electrical resistance of variable resister 32 changes electrical resistance by mechanical movement of the wiper arm attached to the distal float 44 that is responsive to changes in fuel level in the fuel tank 12. The contacts 46 of the saddle 52 are adapted for contacting specific contacts 48 of the variable resistor 32 electrically bridging across to the neutral contact 50 as the saddle 52 and arm 38 sweep there across to complete the variable resistor circuit.
As the level of fuel within the fuel tank 12 changes, the float 44 and wiper arm 38 move and thereby cause the saddle 52 to slide over the arcuate resistive contacts to change an effective length of the variable resistor 32 between the terminals and thereby vary the effective resistance of the variable resistor 32. In accordance with the change in resistance, the current or voltage across the resistor card changes and, thus, effects a change—such as from “Full” toward “Empty”—in a remote fuel level indicator (not shown).
In use, resistive areas and conductive contacts 48 of the variable resistor 32 are generally exposed to the harsh fuel environment in the fuel tank 12. Heptane fuels and especially those containing alcohol supplements can erode the resistive areas and conductive contacts 48, 50 causing sporadic or noisy fuel level indication/measurement. Expensive manufacturing techniques such as the application of coating to the resistor assembly and special housings must be applied to limit erosion. Moreover, existing fuel level sensors can perform erratically when a wiper contactor 46 falls in between, and momentarily out of contact with adjacent, and worn, contacts 48 of the variable resistor 32. In other words, a portion of the variable resistor is momentarily opened or interrupted, thereby causing voltage or current spikes to be output from the fuel level sensor to a liquid level indicator. This problem increasingly occurs as the conductive contacts 48 and edges of the wiper contactors 46 wear out. Another problem involves “catching” of wiper contactor corners on angled conductive contacts 48. When a saddle 52 sweeps across the resistive contacts 48, the sharp corners of the contactors can “catch” on the angled conductive contacts 48, thereby causing noisy operation of the variable resistor 32.